class FileSystem:
    class Dir:
        def __init__(self):
            self.dirs = {}
            self.files = {}
    
    def __init__(self):
        self.root = self.Dir()
    
    def ls(self, path: str) -> List[str]:
        t = self.root
        files = []
        
        if path != "/":
            d = path.split("/")

            for i in range(1, len(d) - 1):
                t = t.dirs[d[i]]
            
            if d[-1] in t.files:
                files.append(d[-1])
                return files
            else:
                t = t.dirs[d[-1]]
        
        files.extend(t.dirs.keys())
        files.extend(t.files.keys())
        files.sort()
        return files
    
    def mkdir(self, path: str) -> None:
        t = self.root
        d = path.split("/")
        
        for i in range(1, len(d)):
            if d[i] not in t.dirs:
                t.dirs[d[i]] = self.Dir()
            t = t.dirs[d[i]]
    
    def addContentToFile(self, filePath: str, content: str) -> None:
        t = self.root
        d = filePath.split("/")
        
        for i in range(1, len(d) - 1):
            t = t.dirs[d[i]]
        
        if d[-1] not in t.files:
            t.files[d[-1]] = ""
        t.files[d[-1]] += content
    
    def readContentFromFile(self, filePath: str) -> str:
        t = self.root
        d = filePath.split("/")
        
        for i in range(1, len(d) - 1):
            t = t.dirs[d[i]]
        
        return t.files[d[-1]]

class FileSystem {

    class File {
        boolean isfile = false;
        HashMap < String, File > files = new HashMap < > ();
        String content = "";
    }
    
    File root;
    public FileSystem() {
        root = new File();
    }

    public List < String > ls(String path) {
        File t = root;
        List < String > files = new ArrayList < > ();
        if (!path.equals("/")) {
            String[] d = path.split("/");
            for (int i = 1; i < d.length; i++) {
                t = t.files.get(d[i]);
            }
            if (t.isfile) {
                files.add(d[d.length - 1]);
                return files;
            }
        }
        List < String > res_files = new ArrayList < > (t.files.keySet());
        Collections.sort(res_files);
        return res_files;
    }

    public void mkdir(String path) {
        File t = root;
        String[] d = path.split("/");
        for (int i = 1; i < d.length; i++) {
            if (!t.files.containsKey(d[i]))
                t.files.put(d[i], new File());
            t = t.files.get(d[i]);
        }
    }

    public void addContentToFile(String filePath, String content) {
        File t = root;
        String[] d = filePath.split("/");
        for (int i = 1; i < d.length - 1; i++) {
            t = t.files.get(d[i]);
        }
        if (!t.files.containsKey(d[d.length - 1]))
            t.files.put(d[d.length - 1], new File());
        t = t.files.get(d[d.length - 1]);
        t.isfile = true;
        t.content = t.content + content;
    }

    public String readContentFromFile(String filePath) {
        File t = root;
        String[] d = filePath.split("/");
        for (int i = 1; i < d.length - 1; i++) {
            t = t.files.get(d[i]);
        }
        return t.files.get(d[d.length - 1]).content;
    }
}